Page 2577 - Hematology_ Basic Principles and Practice ( PDFDrive )

2300 Part XIII Consultative Hematology

venatorum, has caused infection in a small series of older men who intestinal disturbances are common, and people may complain of
261
had undergone splenectomy for a lymphoproliferative disease. The dark urine secondary to hemoglobinuria. In some cases the disease
same organism has been isolated in a much larger series of patients progresses with respiratory failure secondary to ARDS, disseminated
from China. 262 intravascular coagulation, and renal failure requiring the appropriate
273
B. microti and B. duncani have been transmitted by blood and supportive care. Such severe cases resemble severe malaria in
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platelet transfusions. Transplacental infection by B. microti has also nonimmune persons, and it has been suggested that the pathophysiol-
been reported. ogy, like in malaria, includes adhesion and sequestration of infected
erythrocytes and the release of proinflammatory cytokines. These
diseases may be confused with falciparum malaria, leptospirosis, or
Parasitology viral hepatitis. In pregnancy, acute babesiosis may mimic the HELLP
syndrome (hemolysis, elevated liver enzymes, and low platelet
Parasites appear to be introduced into the bloodstream, where they count). 273
invade erythrocytes. There they multiply by asexual fission to produce
two to four merozoites. These infective forms are released after lysis
of the erythrocyte and begin another cycle of invasion multiplication. Hematologic and Laboratory Features
Parasites are cleared by macrophages. The contribution of antibodies
and cell-mediated immune response has not been defined, although The hematologic features of the disease are dominated by substantial
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B. bovis expresses clonally variant antigens on the surface of infected intravascular hemolysis. Physical examination shows pallor, jaun-
erythrocytes. 27 dice, and mild hepatosplenomegaly.
The laboratory findings are those of a compensated intravascular
hemolytic anemia and thus feature low hemoglobin and haptoglobin
Clinical Features levels, increased reticulocyte count and serum lactate dehydrogenase,
and hemoglobinuria and proteinuria. Moderate thrombocytopenia is
The North American B. microti infections have an incubation period common. 265,274 Electron microscopy suggests uninfected erythrocytes
of several weeks, and after infection by blood transfusion, clinical are damaged during infection and so likely to be cleared more rapidly
275
symptoms have taken from 17 days to many months to become than normally. The white blood cell count is usually decreased
manifest. 263–265 The spectrum of clinical disease is wide. B. microti with atypical lymphocytosis and occasional evidence of hemophago-
may cause asymptomatic infection or present with a mild flulike cytosis. However, leukocytosis may occur, particularly in B. divergens
illness in most cases in people with normal immune and splenic infections.
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function. The cardinal manifestations are fever and hemolytic The direct Coombs test result is frequently positive for both C3
anemia. Splenectomy, old age, and immunosuppression, including components and IgG. Polyclonal hypergammaglobulinemia is seen,
HIV, may increase the risk for more severe clinical disease. 267–269 The and levels of C3 and C4 are reduced in acute infection. Liver function
disease may progress to adult respiratory distress syndrome (ARDS), tests show raised indirect bilirubin and mildly raised transaminase
262
disseminated intravascular coagulation, or renal failure. Patients levels.
who have had a splenectomy should avoid exposure to ticks in forested
areas where the disease is transmitted.
B. divergens in Europe predominantly causes symptomatic infec- Diagnosis
tion in people who have had a splenectomy. 270,271 Here, the case
fatality rate is on the order of 50%. However, symptomatic disease The blood films stained with Giemsa or Romanowsky stain show
does also occur in immunocompetent individuals. 272 ringlike intraerythrocytic parasites. Morphology is variable, and ring,
Patients present with high fever, often with chills and sweats, rod, and ameboid forms of Babesia parasites may be seen (Fig.
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jaundice, fatigue, malaise, headache, arthralgia, and myalgia. Gastro- 158.16). Occasionally, multiple intraerythrocytic forms can be

A B

Fig. 158.16 BABESIA PARASITES. Human infection with species of piroplasm transmitted by the bite of
the tick Ixodes ricinus infected from cattle is a rare occurrence. Infection in normal people with this piroplasm
may give rise to a self-limiting fever and parasitemia, as in the case of infection with the rodent parasite Babesia
microti on the northeastern seaboard of the United States via the tick Ixodes scapularis (A). Heavy red-cell
infection may develop, however, in splenectomized patients, leading to fatal hemolytic anemia. This patient
died as a result of an infection acquired from the cattle parasite Babesia divergens in Scotland (B). Other species
of Babesia that occasionally infect humans, for example, the WA1, CA1, and MO1 isolates from the United
States, are distinguished by molecular means.